Many years ago I could not access the apple developer panel because of the umlaut in my last name. It was eventually fixed but I was quite surprised that such a large company would run into such a basic issue.
My last name has an apostrophe in it which Apple apparently loves to embed directly into their JavaScript unescaped. For a long time neither I nor Apple could look up AppleCare status on my stuff as they were all linked to my Apple ID. The portal would thus require me to login, but then would just show a partially rendered page as my last name was causing an JS syntax error.
I love to enter it and see what each vendor and website's backend does with it.
The Staples Canada website, for example, returns it as ' (HTML escaped) A couple times I've logged in, it seems to escape a new character. I'm currently up to '